The purpose of the proposed research is to determine in detail the dependence ultrasonic attenuation and sound speed on the pathological state of breast tissue. These data are required for an adequate assessment of the potential of ultrasound transmission imaging and computed tomography in breast cancer detection. Freshly excised biopsy specimens will be interrogated by finely focused ultrasound beam, and the transmitted ultrasound will be detected by a phase-insensitive acoustoelectric receiver, thereby eliminating artifacts due to phase cancellation that might invalidate most attenuation measurements previously reported in the literature. The sample holder will be translated in a raster pattern to obtain data at up to 256 locations in the specimen. Data will be obtained over the frequency range 2 to 9 MHz and stored for subsequent analysis. Time-of-flight data will yield ultrasound speed at each location. Detailed histological examination and reporting will enable ultrasonic data to be correlated with the pathological state-this will be performed with unprecedented accuracy of registration. Results of this research will permit an assessment of the potential of ultrasound transmission imaging based on attenuation differences in the breast. They will also be pertinent to the interpretation of B-scan images and computed tomographic images.